The long-term objectives of this program project are to develop computational tools that can be used to extract accurate structural and dynamical information from site-directed spin-labeling (SDSL) studies on proteins. These new tools constitute an essential enabling technology to determine the structures and functional dynamics for a wide range of soluble and membrane-bound proteins and their complexes. As such, these tools should have an immediate and significant impact on SDSL studies of proteins here at Vanderbilt and elsewhere, and we intend to make all software and computational protocols developed in this program project freely available to colleagues at other institutions. The specific aims of this program project are: 1) develop molecular dynamics and molecular modeling protocols to enable us to directly correlate EPR measurements of spin label mobility and accessibility with protein structure and structural fluctuations;2) develop simulation tools and protocols so that EPR measurements of inter-probe distances can be related directly to protein structure;3) develop a general computational protocol so that information obtained in Specific Aims 1 and 2 can be used to build and refine structural models;and 4) apply the tools and strategies developed in Aims 1-3 to SDSL data obtained for T4 lysozyme, a model protein of known structure, for CDB3, a more complex erythrocyte membrane protein that is to date only partially characterized structurally, and for amyloid precursor protein peptides that are not well characterized structurally at this time. These specific protein spectroscopic studies will provide the requisite experimental data necessary to develop and test the computational protocols. This program includes investigators with extensive experience in EPR spectroscopy and SDSL studies of proteins (Beth and Hustedt), membrane protein structure-function studies (Beth, Lybrand, and Sanders), and use of molecular modeling and molecular simulation tools to refine three-dimensional protein structures from distance data obtained from spectroscopic and other biophysical studies (Lybrand and Smith).